Coffee machines have a water supply or storage chamber, a heating system for heating the water, a brewing, boiling or scalding chamber for receiving coffee and feed means for feeding water from the water supply chamber into the brewing chamber. Conventional coffee machines differ as a function of the coffee type to be prepared with the corresponding coffee machine. Thus, in espresso coffee machines water is heated and pumped by means of a pump under high pressure (approximately 10 bar) into the brewing chamber and the coffee is finely ground. In Mocha coffee machines the water is supplied in the form of steam through a rising tube to the finely ground coffee in the brewing chamber. The water is also supplied in the form of steam through a rising tube in the case of filter coffee machines, but it condenses again and reaches the fine or ground coffee as a hot liquid and then, under ambient pressure, slowly passes through the filter.
The heating system of conventional coffee machines normally comprises a solid electric heating unit, which is a heat reservoir with a high heat capacity and therefore thermally inert. On the one hand, this is an advantage, because its temperature only decreases slightly when a given water volume flows through it and removes from it a specific heat energy. However, on the other hand, the high heat capacity is a disadvantage, because a large amount of heat energy must be supplied to the electric heating unit in order to raise its temperature to a desired value. After switching on, the conventional coffee machine requires a preheating time lasting a few minutes before it can prepare the first coffee. This preheating time constitutes an irksome time loss for the user.
In order not to have to reheat the electric heating unit prior to each preparation of coffee, heat energy is supplied to it for as long as the coffee machine is switched on. Thus, in the standby mode, the coffee machine constantly requires energy, which it delivers to the environment in a useless manner. If the coffee machine has been switched off for a time, the complete, solid electric heating unit must be heated even for a single coffee preparation and only part of the energy required for this is actually used for preparing the coffee. Thus, in summarizing, it can be stated that conventional coffee machines make uneconomic use of the time of the user and electrical energy.
The problem of the invention is to provide a coffee machine, which firstly requires no preheating time and secondly consumes no energy in the standby mode.
This problem is solved by the coffee machine according to the invention, as defined in the claims. The concept of the coffee machine according to the invention is based on the fact of using a rapidly reacting heating means and to remove the minimum amount of heat energy from the hot water on its path to the coffee. Table 1 shows a comparison of the heating means according to the invention and those of a conventional coffee machine.
TABLE 1 ______________________________________ Characteristics of the Coffee machine according Conventional heating means to the invention coffee machine ______________________________________ Heat capacity low high Reaction fast slow Temperature change during coffee preparation high ______________________________________ low
Table 1.
The coffee machine according to the invention is to be polyvalent, i.e. able to prepare different coffee types. This means that the parts used along the water path, as regards to the mechanical strength, must be designed for the "worst case", i.e. for high pressure during espresso preparation. The parts used must also be optimized with regards to mechanical and thermal characteristics and in part account must be taken of contradictory criteria, so as to combine them in a compromise solution
The advantages of the inventive coffee machine are inter alia achieved by the combination of the following features. Use is made of a continuous flow heater with a small heat capacity instead of a solid electric heating unit. In order to obtain the desired water starting temperature, use is made of a control loop. Materials and design of the unheated parts along the water path are designed in such a way that they are able to withstand the overpressure of the water and simultaneously remove from said water the minimum possible heat energy. In particular, said unheated parts must have low heat capacities and with respect to water low heat transmission coefficients, whilst simultaneously having an adequate strength.